Method and system for grading articles according to color

ABSTRACT

Tobacco leaf is graded by the steps of passing the leaf before a photo-detector, limiting the wave length sensed by the detector to between 660 and 680 m Mu , preferably 670 m Mu , measuring the remission value of the leaf and classifying the leaf in response thereto at selected predetermined levels of remission value.

United States Patent Asfour [45] Nov. 4, 1975 [54] METHOD AND SYSTEM FORGRADING 2,823,800 2/1958 Bliss 209/11 1.6 ARTICLES ACCORDING o COLOR2,933,613 4/ 1960 Powers.... 209/111.6 X 3,064,136 11/1962 Mann209/ll1.6 X Inventor: Emll Asfour, 21 wenglram 8704, 3,206,022 9/1965Roberts... 209/1 1 1.6 x Herrliberg, Switzerland 3,380,460 4/1968 Fuis209/111.6 X Filed: g 9 3,515,273 6/1970 Seaborn 209/11 1.7

[21] Appl' Primary ExaminerAllen N. Knowles Related US. Application D tAttorney, Agent, or Firm-Murray Schaffer [63] Continuation of Ser. No.235,342, March 16, 1972,

abandoned. [57] ABS RACT LS. Tobacco leaf is graded the steps of passingthe leaf IIBt. Cl. before a photo detector the ave length Fleld ofSearch 356/173, 178, sensed by the detector to between 660 and 680 m a,356/186, 195 preferably 670 m [1,, measuring the remission value of theleaf and classifying the leaf in response thereto at Referemes Cltedselected predetermined levels of remission value. UNITED STATES PATENTS2,678,725 5/1954 Jacobson 209/111.6 14 Clams 4 Drawmg F'gures POWERSUPPLY INPUT J J TRIGGER J PD AMPL. GATE GEN. RELAY 22 PHOTOSENSOR l 22l FILTER 24 I BACK- 2O GROUND CLASSIFYING I FIG. 2 MEANS US. Patent Nov.4, 1975 Sheet 1 of 3 3,917,070

LIGHT \L|GH T GRE'LN GREEN -DARK BROWN 400 20 40 so so 5'00 20 10 so so600 20 40 so so voo m FIG. I

POWER SUPPLY I A G T JJ INPUT J J TRIGGER J PD AMPL. GATE GEN. w RELAY22 PHOTOSENSOR l |=Q\22 I FILTER 24 I I BACK- 2O I GROUND CLASSIFYINGFIG.Z E E a l US. Patent Nov. 4, 1975 Shee t 2 of3 3,917,070

MUI

U.S. Patent Nov. 4, 1975 sheet 3 of3 3,917,070

Qm GI METHOD AND APPARATUS FOR GRADING ARTICLES ACCORDING TO COLOR Thisis a continuation of copending application Ser. No. 235,342 filed Mar.16, 1972, now abandoned.

The present invention relates to a system for grading leaf tobacco andin particular to apparatus for automatically sorting tobacco leafaccording to selected grades.

Although texture, size of leaf, moisture and chemical content are allfactors influencing the taste and smokability of tobacco leaf, it haslong been recognized that leaf may be most easily graded (if not with100% accuracy) for these attributes by its apparent color. Apparentcolor is being defined as that color which the naked eye senses andrecognizes. Within the last decade several attempts have been made toautomatically sort leaf or tobacco product by photo-electricallydetermining their apparent color. Reference may be made to US. Pat. Nos.3,373,870 and 3,380,460 for two such examples. Generally, thedetermination is made by comparison with a given standard such as apreselected leaf, a fixed color plate or a background color. A morerecent system has involved the use of photo-electric means to determinetwo or more of the absolute color values, defined as the value of thetrue color components such as red, green, yellow, etc., which make upthe apparent color of a given leaf, and by classifying a leaf as havingmore or less of any one or more of the given colors. All of thesesystems including the earlier systems are dependent on the determinationof at least one given absolute color and employ photo-electric means tosense the desired color component.

In addition to those factors mentioned earlier which effect itsappearance, tobacco leaf color is modified by such things as the degreeof moisture and level of natural surface wax or germ found in the leaf.Moreover, tobacco leaf is highly perishable and fragile, being subjectto physical and chemical change during storage and handling. Thesefactors are readily observable by the hand picker. However, because theyonly imperceptibly change the actual color they are rarely observableunder a photo-electric sensor which determines true or absolute color.The prior systems are also costly, complex, excessively large, difficultto produce and hard to maintain over long periods of use. Furthermore,these systems provide only a degree of statistical efficiency which isacceptable only in contrast with the cost of hand labor.

It is the object of the present invention to provide an improved systemfor photo-electrically grading tobacco leaf.

It is the object of thepresent invention to provide a system for gradingtobacco which is not dependent upon the determination of the absoluteleaf color.

It is another object of the present invention to provide automatic leafgrading apparatus which is simple, economical and easy to manufactureand use.

It is another object of the present invention to provide automatic leafgrading apparatus which is more efficient and reliable than heretoforeknown.

,These objects as well as others together with numerous advantages willbe observed from the following disclosure of the preferred embodimentsof the invention.

SUMMARY OF THE INVENTION According to the present invention. a methodhas been developed whereby tobacco leaf is graded by the steps ofpassing the leaf before a photo-detector, limit- 2 ing the wave lengthsensed by the detector to. between 660 and 680 m ,u., preferably 670 mu, measuring the remission value of the leaf and classifying the leaf inresponse thereto at selected predetermined levels of remission value.

Further in accordance with the present invention a novel system andapparatus including electronic circuitry is provided to enable ascanning device such as a photo sensor to provide an electrical signalindicative of the light transmission of the article to be converted intoa pulse signal for operating an instantaneous classifying means, only ata given level of light transmission.

Full details of the present invention will be found in the followingdisclosure and the accompanying drawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a graph plotting the levels of remission values of variousspecies of leaf against a wave length range between 400 and 700 m ,u,and

FIG. 2 is a schematic representation of a simple current for carryingout the present invention, and

FIGS. 3a and 3b are a schematic diagram showing greater detail of thecurrent of FIG. 2; FIG. 3 is in two parts, being viewed by connectingsheet a to sheet b so that the arrows ABC coincide.

DESCRIPTION OF THE INVENTION For the purposes of this disclosure it isto be understood that the term transmission is the overall light energyoutput of an object. Light transmission is a conventional measure ofsuch energy and is determined by conventional photometric instruments,quite conventional, and which need not be further described here.Transmission value or synonomously remission value is the proportion oflight energy actually emitted as a ratio of the total energy which mightbe emitted. It is defined as a percent Transmittance is employed todefine the transmission ratio corrected for variations in reflection.

The various species of tobacco leaf vary in light energy transmission,and as would be predicable the yellower varieties, such as the Virginiatobaccos have a high remission value while the Turkish and Burleytobaccos for example, have lower remission values. It has beendetermined, however, that all tobacco have an ascending remission valuewhen correlated to an ascending wave length scale, irrespective ofabsolute color content of the leaf. Thus, as is seen in the graph ofFIG. 1, where several leaf groups of different apparent colors arecompared. The curves represent the average value of homogeneously chosenleaf, not necessarily from differing varieties or species, but eachbeing classified by the eye test as within the same grade. As indicated,curve 10 represents yellow leaf, curve 12 the light brown, 14 lightgreen, 16 green and 18 dark brown.

In conventional classification, bright or yellow leaf is most desirableand is, therefore, virtually never picked out of any grade. The verydark brown or black and dark green leaf on the other hand, are virtuallyalways picked out, while the intermediate colors of light brown, brownand light green are selectively picked or chosen to be retaineddepending on the grade desired. It is to be understood that the fiveclasses of leaf shown in FIG. 1 is only representative of the color oftobacco leaf since many shades lie between the very bright yel- 3 lowsand the very dark browns or blacks.

The curves seen in FlG. 1 are plotted by determining the remission valueat given wave lengths under a standard light intensity. The abscissarepresents the wave length measured in standard angstrom units in p. ofnonometers or r l n m the equivalent of 1m X l Conventionally, thesymbol m ,u is used. Readings were taken between a low value of lessthan 400 m p. and a high valve of over 700 m ,u.. The ordinaterepresents the remission valve, as a percent (70) ranging from zero (0)indicating the absence of energy and one hundred (100) indicating a fullenergy level.

Each of the leaf variety sampled at or below the 400 m [.L wave lengthlevel produced virtually identically and negligible remission values andas the sampling proceeded to higher wave lengths the remission value foreach leaf rose in a positive and almost linear curve. Except for theapparent bright yellow specie the slope of each curve was relativelyshallow and sometimes overlapped with another. The apparent brightyellow is significantly greater in energy level than the other species.

In order to establish the validity of the curves, several similarexamples were made under different degrees of light source intensity. Itwas found that when the light source intensity was increased, either byincreasing the voltage or by increasing the number of lamps, theremission value of the leaf was displaced upward upward on the ordinate.Notwithstanding this displacement, the average values within each groupremained relatively and proportionately the same and the curves of eachgroup rose from a base remission value below 400 m u at the same slope,although there was, in fact, greater space between the remission of onegroup and that of another. For example, the space between the curves oflight and dark green spread out along the ordinate, but, in fact eachstarted from a higher base. This showed that light source intensity hadno effect on the relative remission curves in either slope or valuealthough the various groups exhibited individual upward displacement inabsolute remission values.

A startling and unexpected observation was made with respect to eachspecie in the remission values taken in the wave length range between660 to 680 m ,u. Within this narrow range the remission curve for eachof the selected species, regradless of apparent or absolute color value,clips or falls to an inversion point. Thereafter, it continues its riseat a steeper slope than before. It would appear that the actualinversion point coincides at approximately the 670 m p. value. As it isto be observed, the inversion point for each specie lies at a givenremission value distinct from that of any of the other species, althoughthose for the light green and dark brown samples, lie close to eachother. Since the transmission value or overall energy emission of theleaf is the result of all factors governing light transmission,including absolute color, texture, physical characteristic etc., theinversion point is a distinctive photoprint or clear indication of theapparent color of the leaf. The inversion point of each curve may bechanged by varying the light intensity incident on the leaf, however,since the curves retain their proportional slope and relativeseparations from each other, under any constant light conditions, thereis always an inversion point at approximately 670 m ,u. wave length.Thus, the selective determination of remission values within the rangeof 660 to 680 m ,u. has enabled tobacco leaf to be classified and gradedfor any apparent color.

4 Consequently, the objects of the present invention are met by thenovel method of grading tobacco leaf as to apparent color comprising thesteps of passing the leaf before a photoelectric sensor, limiting theresponse rangeof the sensor within a wave length of 660 to 680 m ,u.,measuring the remission value of the leaf andclassifying the leaf inresponse to selected predetermined levels of remission value.

The advantages of the present invention lie in its simplicity. Various,mechanical, optical and even elec-. tronic devices and methods may beemployed to limit the ranges of the photo-detector within the prescribedwave length, leaving remaining a single variable factor, namely, theproportional voltage indicative of the remission value, which must bemeasured. Broad spectrium photo-detectors may be used and their wavelength band response limited by electronic circuitry. While such devicesare no doubt, easily available, the present invention permits the use ofless sophisticate equipment in that narrow band specialtyphoto-detectors may be employed without complicated auxiliary equipment.It is preferred to employ a photo-detector matched closely to the 660 my. to 680 m uband. Such photo-detectors matched to a i 10 m p. bandwidth are relatively inexpensive, and simple, and present very littleproblem in their use. The photo-detector, of course, is intended toconvert the light energy level incidenton it into a proportionalconstant voltage signal. Since to bacco processing plants havenotoriously unstable light conditions, it may be desired to use a lightinterference filter to more narrowly match the transmitted wave lengthto the optimum operating wave length of 670 m ,u.. Filters operable inhalf band widths or less are available. Suitable electronic circuitrycan be assemblied to provide the comparison and trigger functions. Thebroad concept of the present method is not limited by the choice ofapparatus which may be used and many;

variable embodiments are possible.

The present invention is, however, intended particularly for use in theautomatic grading system described in the aforementioned companionapplication. Since such automatic systems are designed to operate athigh speeds and effect continuous grading of rapidly moving streams oftobacco, a preferred mechanical and elec-, tronic arrangement has beendeveloped which exemplifies the present invention. Reference to theaforementioned application, in the following disclosure of the preferredembodiment is made, as if more fully set forth therein.

As seen in FIG. 2, a schematic layout of a suitable. system for carryingout the present inventionis depicted. A photo-sensor and detector PD,such as that manufactured by the Hamamatsu T V Co., Ltd., HamamatsuCity, Japan, under model number R T V R 424, is located above a table 20or other support, such as the end plate shown in the aforementionedapplication, over which the tobacco leaf T is carried. A light source22, such as an ordinary incandescent bulb or series of bulbs is arrangedto concentrate its light upon the passing leaf. The light source needonly supply an intense light sufficient to reflect a degree of energywhich is easily measurable, otherwise the light source is not critical.However, low voltage lamps such as those common in use in automobiles,provide a safe low heat pro-, ducing light source is extremely efficientand more than sufficient for operation in this invention, since thephoto-sensor-detector is, in any event, only required to sense a portionof the emitted light energy of the leaf;

the remission value comprising a ratio.

Preferably, the lights are 12 volt 45 watt incandescent bulbs, of thetype used in motor vehicles or such,

arranged in series of nine. Thus, they may be directly connected to a110 power source. It has'been found that by arrangement two banks ofnine bulbs to each side of the leaf picking table to be tested, there isprovided adequate light for illuminating and providing reflectionsufficient to measure remission. The light banks are generally placed8-12 inches from the table or leaf to be scanned and out of the way ofthe photodetector. They may, if desired, be placed higher. Since only aportion of the light energy is to be measured, the strength of the lightsource need not be great, and interference from ambient or transientlight is relatively negligible. Higher voltage lamps may be used toprovide a higher displaced remission reading, if desired.

Inserted between the photo-cell PD and the table is a filter 24 matchedwith the photo-detector PD to be within the desired wave length rangeand preferably as close to the preferred wave length of 670 m p. aspossible. Metal interference filters, in less than /z% band widths,consisting of two semi-transparent metallic coated mirrors separated byan absorption free intermediate film, (dielectric) the thickness ofwhich determines the spectrum band are preferable. Such filters, forexample, are manufactured by Balzers Aktiengesellschaft, Lichtenstein,under the trade name Filtraflex" and are available in the US. The filteracts to insure a one parameter photo-optic system in which the functionof the photo-detector is solely to register the level of remission.

The photo-detector PD is easily connected to an amplifier circuit Awhich amplifies the voltage produced by it, and then passed to acomparison circuit CC which has an electronic gating subcircuit G presetby a biasing voltage level control L to a desired voltage indicative ofthe standard level of light remission sought. The gate may be designedto open or close on the reaching of this biasing level by thephoto-detector, or in the alternative, on either falling below or abovethis level, as may be desired. It is preferred that it function toprovide a pulse signal when the remission voltage drops below a levelindicative of a given inversion point. Upon actuation of the gate aswitching or trigger circuit T operates relay means R for classifyingthe leaf by ei- I ther removing the leaf from the table or letting itremain thereon, as is shown in the companion application.

The comparison circuit CC may be set at the desired operational voltagearbitrarily by merely providing it with a variable voltage source whichwould control the gate. It is only necessary to initially condition thegate and it need not be periodically recalibrated or continuouslybrought to such a standard condition. This is so, because thephoto-detection apparatus is matched and fixed at a given wave lengthand reads remission value only as a proportional output at the selectedinversion prints. 'The only variable in the system of detection is theremission value of the leaf scanned and therefore, the gate may bepreset at the level of inversion desired and thereafter left alone.Presetting the gate with a fixed biasing voltage, arbitrarily attained,would be simple electronically but would complicate the grading processas a whole, since such a level, being arbitrary, would not be directlyindicative to the actual leaf grade on the table. Accordingly. it ispreferred that the biasing voltage be obtained by setting the gate levelas a result of a fixed background plate over which the leaf passes.Thus, the background plate s own remission value can initially conditionthe system, so that only remission variations in leaf scanned willdirectly cause operation of the trigger mechanism. Spurious andextraneous signals are eliminated to a great extent, by this system. Theconventional colored background plate may be used, although color perse, is no longer critical. The preferred biasing or preset condition ismade through the photo-detector itself, which senses only remissionvalue rather than color. Therefore all that is required is a backgroundplate having a light energy transmission ratio comparable to the leafgrade to be selected. It may be of any color, in fact, in the companionapplication the background plate is made of a shuttered assembly of awhite plate having a plurality of holes overlying a plate having blackdots. A glass overlayer is used to space the leaf from the white plate.By adjusting the two plates, various degrees of white and black areobtained, varying the light transmission ratio. Other similar devicesand constructions may be employed which can establish a desiredremission value. It will also be obvious that once the biasing voltageis set to the initial background transmission level the plate is nolonger of any significance in the detection process. It may if desiredbe removed.

It will thus be seen that by the use of the general apparatus describedin FIG. 2, the method of sensing the leaf at a given limited wavelength, determining the transmission ratio at that wave length, andactuating a classifying means in response thereto can be easilyobtained, and that many suitable circuit arrangements can be made, allwithin the skill of the artisan in these fields. A preferred circuitarrangement is, however, shown in FIG. 3.

The electronic system of FIG. 3 comprises a power pack PP, connected viaa main switch S and a fuse F1 to a common source of AC current. Thepower pack PP is adapted to have a rectified output of poled 15 voltsDC. One of the advantages of the present apparatus is that it lendsitself to ready adaption to printed and integrated circuit design. Inthis event a secondary rectifying circuit RC may be included to insureagainst unwanted interference in each of the printed circuit boards.

The cathode of the photo-detector PD, such as the Hamamatsu, describedearlier, is connected to the negative power source terminal and itsoutput lead connected to the operational amplifier circuit A adapted toproduce an amplified voltage signal directly responsive to the remissionvalues sensed by the photodetector PD. The amplifier circuit comprises aknown integrated transistorized circuit IC (for example, such as thatmanufactured by Teledyne Philbrick Nexus, Allied Drive at Route 128,Dedham, Mass. catalogue No. 1020). The integrated circuit comprises anarrangement or transistors, resistors, capacitors etc., forming achopperless differential amplifier. The operational amplifier IC hasdual inputs a and b and an output 0. The internal contents of the deviceIC, is not shown as the device is produced as a commercial package andis well known. In general, the biasing voltage for the amplifier isprovided through the a terminal and the offset voltage through bterminal. The current through the amplifier circuit is the differencebetween the two inputs and takes the polarity of the highest input. Suchdevices operate at extremely low voltage and current inputs and areextremely sensitive to change in current flow alnected to the offsetterminal b of the amplifier 1C The operational amplifier /.C is set by apotentiometer P together with resistors R 1' and condenser providf ing avoltage divider circuit having noise reducing and feed backcharacteristics. The operational amplifier 1C is thus limited to adesired voltage range by adjustment of the potentiometer P bringing thevoltage range closer to the operational range of the remission valuesactually measured; The biasing terminal a of the operational amplifier1C, is connected to ground so that a constant low biasingvoltage isimpressed which would not interfere with the transmission of theremission voltage current through the operational amplifier.

The output of the operational amplifier is passed directly to the gatingcircuit G, that is, to the offset terminal b of another integratedtransistorized amplifier circuit 1C of the same type as the operationalamplifier 1C The biasing input a of the gating amplifier 1C is connectedto a potentiometer P and a stepping switch W in series with it. Theoutput c of the gating amplifier 1C is connected with a condenser C,which normally blocks unipolar current flow from the gating amplifier 1CThe level of biasing voltage input at terminal a of the gating amplifier1C is preset by the combination adjustment of the potentiometer P andthe stepping switch W, to a level just above that of the remissionvoltage of passable or good leaf to be scanned. Thus polarity reversalwill occur only if the remission voltage is less than that of a goodleaf, namely, occurring at or below the inversion point. This biasingvoltage is obtained by initially setting a background plate of desiredlight transmission characteristics beneath the photodetector.Preferably, the light transmission is equal to the lowest good qualityleaf to be passed by the detector. The photo-detector thus produces aunipolar volt.- age indicative of the grade of bad or unwanted leaf tobe rejected. This voltage is passed, as explained, through theoperational amplifier 1C to the offset input b of the gating amplifier1C The potentiometer P and stepping switch W are then adjusted to raisethe voltage level on the biasing input a to a point just above theoffset level. As soon as a level of voltage greater than that of theoffset voltage is received, the gating amplifier 1C will reverse inpolarity tripping the condenser C If maintained in this state thedetection system will pass good leaf and sense only bad leaf having avoltage less than that of the biasing voltage. The combinedpotentiometer P and stepping switch W voltage is set to provide abiasing voltage at a current of only a few .millivolts above that of theremission value at the inversion point or to a slightly better levelthan the inversion point of the leaf grade to be rejected. In thismanner the gating amplifier 1C runs constantly at remission voltagessubstantially equal to the background plate and allows all good leafpassing the photo-detector, but reverses polarity and current flow onthe production of a remission value which fall below the pre determinedamount set on the biasing input, thus rejecting bad leaf.

The-tripping of the condenser C by reversal of the gating amplifier 1Cproduces a pulsing signal in line P.S. passing through a normally closedcontact k ofa manual switch K into a trigger circuit T adapted tooperate a solenoid relay U which operates switch contacts U and Uadapted to actuate a pair of solenoid air valve rejectors. See FIG. 3a.'As will be noted the gate G functions by maintaining ..a constantvoltage level at a given polarity at the biasing input..As soonas thisvoltage level becomes greater than the offsettingvoltage, the polarityof the gate amplifier 1C changes, producing the pulse signal through thecondenser. To insurethat the gate amplifier again reverses its polarityto permit the sensing of succeeding leaf, the solenoid U has a switchcontact U arranged with the control potentiometer P and stepping switchW which instantly causes the gate G to reverse polarity. This resettingoperation, it will be noted, is not a recalibration of the compressionvoltage since the calibration voltage never varies and remains the same,as the position of the potentiometer P and stepping switch W is notchanged. The resetting operation merely permits the instantaneousreestablishment of dominance of the offset poled voltage on the gate Gto permit the next voltage signal from the amplifier A to be passed tothe gate 1C without delay. In fact, the resetting operation is so swiftthat the speed of the conveyor movement described in the aforementionedpatent can be raised to well over 1000 ft./minute, without anymis-detection caused by electronic delay.

The potentiometer P is necessary only when one or more photo-cell unitsare used in conjunction with a single table. Since there are inherentvariances in photo-detection cells, even under the most carefulmanufacturing standards, the individual cells must be matched againsteach other. Potentiometer P permits this matching by allowing each cellto be individually set at a predetermined selective level. Themultiposi' tion stepping switch W is connected in series to the potentiometer P each contact being connected to a resistor of differentvalue than the other. A switch S- is inserted in the line so as topermit the multiposition stepping switch W to be cut-out when thepotentiometer P is being initially adjusted. When several photodetectingunits are employed as indicated above, the stepping switches of each maybe mounted on a com mon shaft so that they may be provided with a commonsetting.

The purpose of the stepping switch is to allow the ad justment of thebiasing voltage level on bias input a of the gate G to be set independence on the background plate corresponding to grade to be scanned,and to per mit this adjustment for all the photo-detectors employed inunison on a single table. Since the entire circuit operates in the lowvoltage ranges and in milli ampere currents the stepping switch need begraduated only in very small voltage increments. Once the steppingswitch is calibrated for the particular grade it may be locked intoplace and operation of the table commenced and conducted indefinitely.Similarly, the background plate may be removed as soon as the step pingswitch is properly fixed, since the biasing voltage on input a of thegating amplifier will not change. However, the background plate is keptin place in order to insure'that the same light and transmissionconditions through the operation occur.

The trigger circuit T comprises a silicon power unidirectionaltransistor T in a two stage resistor-capacitor coupled circuitarrangement, the operation of which will be evident. An array of timingresistors and condenser bridge the transistors T and T to provide a timedelay circuit to hold the signal for a predetermined time interval. Thetrigger circuit operatesthe s0- lenoid relay U which is bridged byadiode D limiting: i

current flow through the circuit. to insure against .transient orspurious excess current from the-pulse signal,

The solenoid relay controls contacts U and U which,

actuate the solenoid air valves v -and 2V controlling the air ejectionmeans andthelplate air cleaning blasts respectively, described in I thecompanion application. I

The solenoid U also controlsa' switching 'contactUg,

which alternates between contact withthe potenti o'mek. ter P and thestepping s'witch'W t verse the polarity on the stepping switch andpottiofri'eter; P5

voltage signal. The sol'e'r'i'oid r'elay Contact 'U i rnally closed incontact with 'steppiii'g switch; and moves'into contact withpotentiometer Pgonactuation;

Leading from the output of thefoperational amplifier 1C and bypassingthe gate amplifier is alead to the meter circuit. This circuit comprisesan integrated transistorized amplifier circuit 1C similar to those notedabove. It includes its own potentiometer P which is adjusted to set thelevel of voltage to the meter and a suitable feed back and compensatingresistorcondenser components.

The manual switch K is adapted to open the contact k and inserting via asecond contact k the meter M bypassing the gate G so that the actualvalue of the voltage indicative of the remission value may be read. Theswitch k has a third contact k which simultaneously closes a lightcircuit having a lamp L indicating the operation of the meter and thebypassing of the gate G.

Connected to the normally closed portion of contact U, of solenoid relayU is an indicating lamp L A green light may be used as it will bemaintained lit when the detector senses good leaf. Connected to thenormally closed portion of the contact U is another lamp L indicatingthe reversal of the solenoid U and consequently the presence of a signalpulse through the gate G. It may be red. The red signal indicates thedrop of remission value lower the inversion point and conse quently thepresence of a bad leaf.

It will thus be seen that the present invention provides a simple yethighly improved method of sensing and sorting leaf into various grades.The circuitry and electronic apparatus are highly adaptable to highspeed operation, in line with the basic method of sense leaf basedsolely upon a singly variable factor. Various changes and modificationsare obvious and it is to be understood that the present disclosure isillustrative only and not limiting of the invention.

What is claimed is:

l. A system for grading articles according to apparent color comprisingmeans for supporting said articles, a photo-sensor having detector meansfor sensing the light remission value of each said article, meansrestricting the response of said photo-sensor to a defined wave lengthrange approximately coextensive with the wave length range at which theremission curve of a specific article at ascending wave lengths inverts,said photo sensor producing a signal variable in response to the levelof said light remission in said range, means for converting said signalto a voltage proportional thereto, a gating circuit adapted to convertsaid voltage into a pulse at a given level of said voltage. triggermeans responsive to said pulse. and classifying means responsive to saidtrigger means for removing said article from said support.

r 10 i 2The systemaccording to claim 1 including means for providing aninitial source of light remission of a given value, andmeansforficoordinating said gating cir-" cuit thereto to cause onlyarticles of a remissivity differ ent from said given value-to besorted.

3. The system according to claim 2 wherein said means'for providing aninitial source of light 'remission isiadjust-able to selected levelsthereof.

4. Thefsystem accordin'g'ito claim 1' wherein? the means for restrictingthe response of said photo-sensor is limited-to the se nsing oflightfremission in a wave length band of substantially 660 to'rnillimicr'ons.

5. The system according to claim including means for controlling thegating circuit topas'sa pulsevoltage on sensing the inversion in said'e'u'rve;

6. The'system accbrdingto claim 5 including'an adj justable signallimiting i'riea'ns asbiarw with said gating means for establishingaselected level of electrical si'grialto provide saidjvol'tag epul se." F

7. Apparatus for continuously and automatically grading leaf tobaccocomprising means for conveying an endless stream of spaced tobaccoleaves, means for illuminating each said leaf with a broad-spectrumlight, a photo-sensor for determining as an electrical signal "the lightremission of each said leaf as it passes said sensor, said photo-sensorbeing limited to respond to wave lengths within a predefined range, afirst amplifier for converting said signal to a voltage proportional tosaid light remission, a second amplifier responsive to said proportionalvoltage comprising a gating circuit including biasing means for passinga voltage of a predetermined level relative to the level of voltageobtained at the inversion point of the curve of light remission of apredefined leaf, a circuit adapted to convert the voltage of saidpredetermined level into a pulse signal, a trigger circuit includingsolenoid means responsive to said pulse signal for operating a leafclassifying means adapted to divert said leaf producing said pulsesignal. 8. The apparatus according to claim 7 wherein said biasing meanscomprises at least one variable resistor. 9. The apparatus according toclaim 7 wherein said circuit adapted to convert the voltage into a pulsesignal includes a condenser and means operable by said Solenoid torestorethe state of said condenser simultaneous with the operation ofsaid leaf classifying means. 10. In a system for continuously andautomatically grading random leaf tobacco into acceptable andnonacceptable classes, comprising moving said leaves in a continuousstream at random orientation to a sensing station, illuminating saidsensing station with a broad spectrum light source, locating aphoto-sensor at said sensing station, limiting the normal response ofsaid photo-sensor to a wave length range within predefined limits, saidphoto-sensor providing a signal indicative of the light remission ofeach leaf as it passes said station within said predefined limits, agating circuit responsive to said signal, said gating circuit includingmeans for limiting its response to a level corresponding to the point ofinversion of said light remission at ascending wave lengths, meansconverting said voltage passed by said gating circuit into a pulsesignal, pneumatic means arranged at said sensing station responsive tosaid pulse to remove said leaf from said station on determination of avoltage corresponding to said point of inversion. 11. The systemaccording to claim 10 wherein a plurality of photo-sensors are arrangedat said sensing station each scanning a separate portion thereof andeach 1 1 connected to a separate amplifier, gating and pneumatic means.

12. A system for grading articles according to apparent color comprisinga photo-sensor having detector means for sensing the light remissionvalve of each said article, means restricting the response of saidphotosensor to a defined wave length range approximately coextensivewith the wave length range at which the remission curve of a specificarticle at ascending wave lengths inverts, said photo-sensor producing asignal variable in response to the level of said light remission in saidrange means for converting said signal to a voltage proportionalthereto, a gating circuit adapted to convert said voltage into a pulseat a given level of said voltage, and classifying means responsive tosaid pulse for sorting said articles.

13. A system for grading articles according to apparent color comprisinga photo-sensor having detector means for sensing the light remissionvalue of each said article, means restricting the response of saidphotosensor to a defined wave length range approximately coextensivewith the wave length range at which the remission curve of a specificarticle at ascending wave lengths inverts, said photo-sensor producing asignal.

variable in response to the level of said light remission in said range,a circuit responsive to said signal and adapted to produce a triggersignal at a given level of apparent color and wherein said circuit isresponsive to both said first signal and said reference voltage level toproduce said trigger signal.

1. A system for grading articles according to apparent color comprisingmeans for supporting said articles, a photo-sensor having detector meansfor sensing the light remission value of each said article, meansrestricting the response of said photosensor to a defined wave lengthrange approximately coextensive with the wave length range at which theremission curve of a specific article at ascending wave lengths inverts,said photosensor producing a signal variable in response to the level ofsaid light remission in said range, means for converting said signal toa voltage proportional thereto, a gating circuit adapted to convert saidvoltage into a pulse at a given level of said voltage, trigger meansresponsive to said pulse, and classifying means responsive to saidtrigger means for removing said article from said support.
 2. The systemaccording to claim 1 including means for providing an initial source oflight remission of a given value, and means for coordinating said gatingcircuit thereto to cause only articles of a remissivity different fromsaid given value to be sorted.
 3. The system according to claim 2wherein said means for providing an initial source of light remission isadjustable to selected levels thereof.
 4. The system according to claim1 wherein the means for restricting the response of said photo-sensor islimited to the sensing of light remission in a wave length band ofsubstantially 660 to 680 millimicrons.
 5. The system according to claim4 including means for controlling the gating circuit to pass a pulsevoltage on sensing the inversion in said curve.
 6. The system accordingto claim 5 including an adjustable signal limiting means associated withsaid gating means for establishing a selected level of electrical signalto provide said voltage pulse.
 7. Apparatus for continuously andautomatically grading leaf tobacco comprising means for conveying anendless stream of spaced tobacco leaves, means for illuminating eachsaid leaf with a broad-spectrum light, a photo-sensor for determining asan electrical signal the light remission of each said leaf as it passessaid sensor, said photo-sensor being limited to respond to wave lengthswithin a predefined range, a first amplifier for converting said signalto a voltage proportional to said light remission, a second amplifierresponsive to said proportional voltage comprising a gating circuitincluding biasing means for passing a voltage of a predetermined levelrelative to the level of voltage obtained at the inversion point of thecurve of light remission of a predefined leaf, a circuit adapted toconvert the voltage of said predetermined level into a pulse signAl, atrigger circuit including solenoid means responsive to said pulse signalfor operating a leaf classifying means adapted to divert said leafproducing said pulse signal.
 8. The apparatus according to claim 7wherein said biasing means comprises at least one variable resistor. 9.The apparatus according to claim 7 wherein said circuit adapted toconvert the voltage into a pulse signal includes a condenser and meansoperable by said solenoid to restorethe state of said condensersimultaneous with the operation of said leaf classifying means.
 10. In asystem for continuously and automatically grading random leaf tobaccointo acceptable and non-acceptable classes, comprising moving saidleaves in a continuous stream at random orientation to a sensingstation, illuminating said sensing station with a broad spectrum lightsource, locating a photo-sensor at said sensing station, limiting thenormal response of said photo-sensor to a wave length range withinpredefined limits, said photo-sensor providing a signal indicative ofthe light remission of each leaf as it passes said station within saidpredefined limits, a gating circuit responsive to said signal, saidgating circuit including means for limiting its response to a levelcorresponding to the point of inversion of said light remission atascending wave lengths, means converting said voltage passed by saidgating circuit into a pulse signal, pneumatic means arranged at saidsensing station responsive to said pulse to remove said leaf from saidstation on determination of a voltage corresponding to said point ofinversion.
 11. The system according to claim 10 wherein a plurality ofphoto-sensors are arranged at said sensing station each scanning aseparate portion thereof and each connected to a separate amplifier,gating and pneumatic means.
 12. A system for grading articles accordingto apparent color comprising a photo-sensor having detector means forsensing the light remission valve of each said article, meansrestricting the response of said photo-sensor to a defined wave lengthrange approximately coextensive with the wave length range at which theremission curve of a specific article at ascending wave lengths inverts,said photo-sensor producing a signal variable in response to the levelof said light remission in said range means for converting said signalto a voltage proportional thereto, a gating circuit adapted to convertsaid voltage into a pulse at a given level of said voltage, andclassifying means responsive to said pulse for sorting said articles.13. A system for grading articles according to apparent color comprisinga photo-sensor having detector means for sensing the light remissionvalue of each said article, means restricting the response of saidphoto-sensor to a defined wave length range approximately coextensivewith the wave length range at which the remission curve of a specificarticle at ascending wave lengths inverts, said photo-sensor producing asignal variable in response to the level of said light remission in saidrange, a circuit responsive to said signal and adapted to produce atrigger signal at a given level of said first signal, and classifyingmeans responsive to said trigger signal.
 14. The system as in claim 13further including means for selectively setting a reference voltagelevel at a value corresponding to the inversion level at said definedwavelength range of an article having a desired apparent color andwherein said circuit is responsive to both said first signal and saidreference voltage level to produce said trigger signal.